Method and apparatus for treating injection-moulded objects in a production process

ABSTRACT

A method for treating workpieces ( 307, 801, 802, 803 ) to be injection moulded in a production process comprises a step for forming a workpiece ( 307, 801, 802, 803 ) by injection moulding so that during the injection moulding, the workpiece is fastened to a given elongated transport arrangement ( 301, 302, 304, 305, 306 ). The workpiece ( 307, 801, 802, 803 ) is moved forwards in the production process by means of the elongated transport arrangement ( 301, 302 ). Subsequently the fastening ( 311 ) of the workpiece ( 307, 801, 802, 803 ) is partly detached from the elongated transport arrangement ( 305, 306 ) and the workpiece ( 307, 801, 802, 803 ) is fastened, supported by the fastening remaining between itself and the transport arrangement, into a position where it is substantially outside a plane ( 800 ) defined by the transport arrangement.

The invention relates generally to serial production of workpieces byinjection moulding and to their treatment subsequent to theinjection-moulding step of the production process. The invention relatesspecifically to the combination of the workpieces and the arrangementmade for their transport so as to allow versatile handling of theworkpieces.

Finnish Patent Application No 963873 discloses a production process andapparatus, in which semi-finished workpieces are connected in successionand possibly also in parallel by connecting bridges. FIG. 1 shows howthe workpieces produced in a given production step from an elongatedcontinuous band, which is wound up in a roll 4. Regarding the example ofthe figure, it is conceivable that the raw material used isinjection-moulded plastic and the products 1 to be prepared are smallplastic objects. For the successive objects not to be detached, the jawsof the clamp in FIG. 3 have been shaped so that the “rear end”(right-hand end in the figure) of each workpiece will comprise a smallplastic tongue, which is superfluous in terms of the shape intended forthe product. When the following workpiece is injection moulded, a smallplastic tongue will also be formed at its “front end” (left-hand end inthe figure), the tongue being superfluous in terms of the shape intendedfor the product and being fastened by melting to the tongue at the rearend of the preceding workpiece. A bridge 2 made of the same material asthe actual work-pieces will be formed between the successive workpieces.

FIG. 2 illustrates the surface treatment included in the same productionprocess. The band formed of workpieces is brought to the surfacetreatment wound up as a roll 6. The workpieces are guided as a band to adip varnishing basin 7, and from there on to surface paint spraying 8and to a drying machine 9. Other surface treatment steps given by way ofexample and illustrated in FIG. 3 are printing 10, gluing 11 of asticker or a label, and laser production 12 of an identifying pattern.Two optional operations are presented as the last step in the figure. Inthe first option, the laser cutter 13 separates the workpieces 15 fromthe band, and after this they have to be handled as individual pieces ingeneral. In the second option, the finished workpieces are further woundup as a roll 14 or bent into a pile, allowing them to be readilytransported and placed in the assembly step of a more complex product.

Nonetheless, the prior art method described above has proved awkward inthe practice, because the bridges made of injection-moulded material andconnecting the successive workpieces do not withstand all process stepsproperly. In addition, they limit the handling of the band of workpiecesin some process steps.

The typical feature of production methods based on solidification of aliquid or a viscous production material is that the material is guidedto the desired locations of the mould through one or more “pouringchannels”. In the solidification step, there is still material in thepouring channels, and thus this portion of the material will form asprue. The actual workpiece and the sprue are connected by a thinmaterial bridge at the point where the pouring channel has beenconnected to the mould of the workpiece proper. The sprue is oftenutilised in tie further processing of the workpiece, because e.g.surface treatment intended to cover the entire workpiece surface is easyto carry out by holding the sprue. U.S. Pat. No. 5,478,051 discloses amethod in which the plastic parts to be injection moulded, after havingbeen pressed, form a band, in which a separate reinforcing wire passesthrough the sprues and connects successive parts. The publicationdescribes both embodiments in which the wire consists of the samematerial as the injection-moulded pieces and embodiments in which thewire is e.g. a metal wire. Similar solutions are disclosed in patentspecifications U.S. Pat. Nos. 4,008,302 and 3,192,298.

However, the solutions above are disadvantageous in terms of theirmanufacturing techniques, because they cannot be subjected to, say, dipvarnishing, without the band assisting also in the transport or anyother auxiliary equipment being immersed in varnish. Thus, the auxiliaryequipment will usually be fit for use only once, because recycling ofthe equipment would result in detrimental varnish accumulation in theapparatus.

The object of the present invention is a method and an apparatus forproducing injection-moulded workpieces so as to allow versatile furtherprocessing of the workpieces without a disposable transport arrangement.Another object of the invention is to allow the workpieces to be exactlyaligned in the different steps of the production process.

The objects of the invention are achieved by providing the workpieceswith fasteners enabling them to be connected to the transportarrangement so that the fastening can be partly released, and then thepartly released fasting allows the workpiece to be shifted in at leasttwo different positions relative to the transport arrangement.

The method of the invention comprises steps for

a) forming the workpiece by injection moulding so that the workpiece isfastened to a given elongated transport arrangement during the injectionmoulding

b) moving the workpiece forwards in the production process by means ofthe elongated transport arrangement.

The method is characterised by comprising steps for

c) partly releasing the fastening of the workpiece from the elongatedtransport arrangement

d) shifting the workpiece supported by the remaining fastening betweenitself and the transport arrangement into a position where it issubstantially outside the plane defined by the transport arrangement

The invention also relates to an apparatus comprising

a mould for producing workpieces by injection moulding

an elongated transport arrangement for moving the injection-mouldedworkpieces forward in the production process;

the apparatus having a mould disposed to form fastening members in theworkpieces for fastening the workpieces to the transport arrangement.

The method is characterised by comprising

means for partly releasing the fastening of the workpieces from thetransport arrangement

means for shifting a workpiece whose fastening to the transportarrangement has been partly released into a position relative to thetransport arrangement, where it is located substantially outside a planedefined by the transport arrangement

In accordance with the invention, fastening members are formed in theworkpieces during the injection moulding to connect the workpieces withthe transport arrangement, which is intended to transfer the workpiecesbetween the different steps of the production process. At least part ofthe fastening members are made removable. Removable fastening memberscan also be formed so that they can be refastened after having beenunfastened. When all the fastening members are fastened, the workpieceshave a specific first position relative to the transport arrangement. Inthis position they are easy to align accurately in a given step of theproduction process, because the fastening members, any separate aligningmembers connected with these, and the parts of the transport arrangementto which the fastening members are fastened, can be used as mechanicalaligning means.

When part of the fastening members have been unfastened, the workpiececan be turned into a second position while being supported by theremaining fastening members. The workpiece can be conceived assubstantially planar, and then the direction of its plane in the firstposition is substantially the same as the direction of a given planedefined by the transport arrangement. In the second position, theworkpiece can be turned so that the direction of its plane deviatesnotably from the direction of the plane defined by the transportarrangement. If the fastened fastening members are at a given edge ofthe workpiece, the workpiece will in its second position, be principallylocated quite far from the plane defined by the transport arrangement,and can then be e.g. immersed in a vessel containing a surface treatmentagent without the transport arrangement getting into contact with thissurface treatment agent.

The transport arrangement considered most advantageous comprises one ormore band-like or chain-like conveyors forming a closed loop. Theconveyor is called a chain for the sake of conciseness. At regularintervals the one or more chains are provided with attachment points,and at each of these a given axis can be fastened. The transportarrangement and the injection-moulding mould are mutually positionedsuch that when the mould is closed, at least one was will remain withinit. Thus fastening members are formed on the injection-moulded workpieceto attach this to at least one axis. It is preferable to fasten theinjection-moulded workpiece to two successive axes, and then at leastthe fastening members attached to one of the axes will be removable.When the fastening is released from one axis, the workpiece will remainsupported by the other axis, and can then be rotated about this axisinto the desired position.

The invention is described below in greater detail with reference to thepreferred embodiments given by way of example and to the enclosedfigures, in which

FIG. 1 shows a conventional arrangement for forming a band of workpieces,

FIG. 2 shows conventional surface treatment of a band of workpieces,

FIG. 3 shows an arrangement of the invention,

FIG. 4 is a lateral view of the workpiece of the invention,

FIGS. 5a-5 c show a number of optional fastener designs,

FIGS. 6a-6 d show a number of optional cross-sections of the axis,

FIGS. 7a-7 f show a number of fastening designs of the axis,

FIG. 8 shows the turning of the workpiece relative to the transportarrangement,

FIG. 9 shows a production process in accordance with the invention,

FIGS. 10a-10 b show an operation of the transport jaws in the apparatusof the invention,

FIGS. 11a-11 b show a number of workpiece details,

FIG. 12 shows a number of optional positions of the pouring channel

FIG. 13a shows the application of the invention to multi-step injectionmoulding,

FIG. 13b is a lateral view of some parts of the workpieces of FIG. 13a,

FIG. 14 shows a detail in the processing of a colour film,

FIG. 15 shows an optional detail in the processing of a colour film,

FIGS. 16a-16 c show some ways of compensating for shrinkage of theworkpiece and

FIG. 17 shows a way of using inserts.

The prior art description above refers to FIGS. 1 and 2, and thus thefollowing description of the invention and its preferred embodimentswill refer mainly to FIGS. 3-17. In the figures, the same referencenumerals will be used for mutually corresponding members.

FIG. 3 is a schematic view of two parallel conveyor chains 301 and 302.The chains are mutually parallel and they consist of a plurality ofsuccessive, mutually identical loops 303. Axes transverse to thelongitudinal direction of the chains have been connected to the chains,with axes 304, 305 and 306 appearing in FIG. 3. The distance between twosuccessive axes is substantially constant. The arrangement for fasteningthe axes to the chains is illustrated in greater detail below.

FIG. 3 further shows four mutually identical workpieces, which have beenmade by injection moulding. By way of example, it is assumed in FIG. 3that each workpiece is intended for the production of a protectivewindow for the display of a small-sized electronic device. To this end,each workpiece has a service member 307, in which the darkened margin308 surrounds the transparent central part 309. To fasten the servicemembers to the axes, each workpiece comprises two upper fasteningmembers 310 and two lower fastening members 311. The fasting members areconnected with the service members by a narrow bridge; the final productno longer comprises any fastening members, since these are detached fromthe service member in an ultimate production process step by breakingthe bridge connecting the fastening member and the service member.

FIG. 4 shows a workpiece viewed in the direction indicated by the arrow312 in FIG. 3. FIG. 4 shows a first axis 305, a second axis 306, aservice member 307, an upper fastening member 310, a lower fasteningmember 311 and a narrow bridge 401 connecting the fastening member andthe service member. FIG. 4 also shows a preferred design of thefastening members: each fastening member comprises at its end facing theaxis a hook 402, which encloses the axis partly. The fact that the upperfastening member 310 encloses the axis from a different side than thelower fastening member 311 has no limiting impact on the invention,however, it yields a number of advantages described below. In thispatent application, the terms “upper” and “lower”, and also the otherexpressions of direction, are merely intended to illustrate the partsbetter in the accompanying figures, and they have no limiting impact interms of the invention.

Instead of the hook shape shown in FIG. 4, the end of the fasteningmember which is connected with the axis can be shaped in other ways aswell. FIGS. 5a-5 c show a number of optional embodiments: FIG. 5a showsa sleeve-like shape encircling the axis completely, which must be atleast partly broken at the stage of detaching the fastening member fromthe axis. FIG. 5b shows a fork-like design, in which the fasteningmember encloses the axis partly from two sides. FIG. 5c shows a variantof the fork-like embodiment, in which one branch 501 of the fork is madeshorter and weaker than the other one, and can thus be cut off while theother branch remains. The remaining branch can be dimensioned with arelatively great length, thus forming a relatively solid fastening evenby itself.

The axis does not have to be circular in cross-section, nor does it needto be constant in cross-section over the total length of the axis. FIGS.6a-6 d show a number of optional cross-sections of the axis, which canbe used either over the total length of the axis, or, for instance, onlyat the points of the axis where the axis is connected with the chains,or at the points where the fastening members of the workpieces areconnected with the axis. FIG. 6a shows an axis which is mainly round butnotched at regular intervals, FIG. 6b shows an axis toothed over itsentire circumference, FIG. 6c shows a notched axis, and FIG. 6d shows anotched axis which is substantially square in cross-section.

The axis may comprise designs at its different locations which areintended to assist in maintaining the axis in position in thelongitudinal direction relative to the chains and/or to maintain thefastening members pertaining to the workpieces in position relative tothe longitudinal direction of the axis. FIGS. 7a-7 f show a number ofsuch exemplifying designs, i.e. various notches, embossments andcombinations of these.

The axis may be fastened to the chains either by a removable or astationary connection. With a view to the manoeuvrability of theworkpiece, the axis is preferably fastened to the chains so as to befreely rotatable about its longitudinal axis. When the fastening of theworkpiece to the axes has thus been partly detached and the workpiece isshifted into a different position relative to the transport arrangement,the rotation may occur either in the connection between the fasteningmember and the axis, or in the connection between the axis and thechain, depending on which connection has lower friction. The chain loopsmay be connected by a special connecting member provided with a hole ora notch for the axis, or part of the chain loops may be so small thattheir central opening leaves only a passage of exactly the size of thecross-section of the axis for this to pass.

Speaking of chains, it should be noted that in terms of the invention,the only criteria for a “chain” are an elongated shape and thepossibility for axes to be fastened at regular intervals. The “chains”may be e.g. bands, to which transverse bushings have been fastened atregular intervals by gluing or any other known method to receiveinserted axes.

FIG. 8 shows a step of the production process which makes benefit of thepartial detachment of the workpieces from the transport arrangement. Theplane defined by the transport arrangement, i.e. the chain plane, isillustrated by the broken line 800, and the direction of movement of thetransport arrangement is indicated with a dashed arrow. A given firstworkpiece 801 is still attached to the axes at both ends. A given secondworkpiece 802 has just been partly detached by its lower fasteningmembers having been ejected from the axis. Owing to the hook shape ofthe fastening members and to the adequate elasticity of the rawmaterial, a given fastening member can be “snapped” out from the axisand, whenever necessary, inserted in the axis again by “snapping”. Whenthe lower fastening members of the workpiece 802 have been detached, theworkpiece can be shifted into another position relative to the plane 800defined by the transport arrangement. The shift is illustrated with acurved arrow. In FIG. 8, the third workpiece 803 has been turned in aposition in which the plane defined by the workpiece forms an angle ofsubstantially 90 degrees to the plane 800 defined by the transportarrangement. In such a position, the workpiece 803 can be varnished orsubjected to any other surface treatment without being immersed into thevessel containing the surface-treatment agent. Since the service memberis relatively far from the chains, these will not be dipped in thesurface-treatment agent.

FIG. 8 shows particularly that partial detachment implies detachmentspecifically of the lower fastening members from the axis, i.e. thefront fastening members viewed in the direction of movement of theworkpieces. However, the invention does not involve any limitations inthis respect, and hence partial detachment can take place in the waybest suited for each situation. Varying partial detachments can beperformed in the different process steps.

FIG. 9 is a schematic view of a production process using the solutionsdescribed above. The plastic raw material is fed through a plasticationunit 901 and a squeezer 902 into a mould, which consists of a first half903 a and a second half 903 b. The mould halves are movable relative toone another. For the injection-moulding step, they are pressed together,and are subsequently separated, and then the injection-moulded workpiececan be detached from the mould and removed for the subsequentinjection-moulding step. The chains 904 form a closed loop, which is fedto the location of the mould by means of aligning and clamping rolls 905and 906. As noted above, the chains themselves do not usually passthrough the mould (even if the invention as such does not exclude suchan option), but in a system of two chains, these pass on either side ofthe mould, and thus only a given number of axes fastened between thechains will remain within the mould during the injection-moulding step.

Step 907 shows a band formed by injection-moulded workpieces. At thisstage, the workpieces are fastened to the axes at both ends. At the roll908, a detaching unit 909 is provided, in which specially designed rollsdetach the fastening of one end of each workpiece. In step 910, theworkpieces are suspended from the transport arrangement by one end only,and are thus easily subjected to surface treatment by dipping them intoa vessel 911. After this, the workpieces may be either allowed to bestill suspended only by one end, or the fastening which has been undonein step 909 can be refastened. Even without refastened, under the forceof gravity, the workpieces will be aligned with the plane defined by thetransport arrangement in such ulterior production process steps wherethis plane is vertical.

FIG. 9 shows the subsequent processing steps of drying 912 andultraviolet curing 913 of the surface-treatment agent. In step 914, theworkpieces are totally removed from the transport arrangement and thechains with their axes start recirculating towards the mould. If theaxes are notably fouled during the process, a step can be added betweensteps 914 and 905, in which the axes are removed, and are either cleanedand refastened to the chains, or replaced with new, clean axes.

The force of gravity can be utilised also otherwise to carry out thefastening between the workpiece and the axes. The fastening memberintended to be detached in a given subsequent production process stepmay consist merely of a projection lying on the axis when the workpieceand the transport arrangement are in a position where the force ofgravity exerted on the workpiece presses this projection against theaxis. As the transport arrangement subsequently turns into a differentposition, e.g. upwards-down compared with the previous position, theworkpieces will drop into a position where they are suspended from theaxis that provides better attachment e.g. with hooks of the shapediscussed above.

FIGS. 10a and 10 b show a preferred embodiment for performing themechanical transfer of the transport arrangement at the injection mould.The mould consists of two halves 903 a and 903 b, which have beenpressed together for the duration of the injection moulding in FIG. 10a.One injection-moulding step usually lasts some seconds. Meanwhile, thetransfer jaws 1001 a and 1001 b move backwards over a given distance:the length of the displacement equals the distance over which thetransport arrangement should move between two successiveinjection-moulding steps. When the injection-moulding step has ended andthe injection-moulded workpiece is sufficiently solidified, the mouldhalves are opened as shown in FIG. 10b. While the mould halves are beingopened, the transferjaws 1001 a and 1001 b are pressed around the chainsand/or axes, and after this the transfer jaws move the assembly formedby chains, axes and workpieces forwards.

Usually the body to be injection moulded is provided with ejection pinsmade of the same material as the remaining body and directed directlyinto either one of the mould halves. This mould half is usually the onewhich does not communicate with the plastication unit and through whichno raw material is thus squeezed (lower mould half 903 b in FIG. 10).Under the action of the ejection pins, the workpiece will remainattached to the mould half facing the ejection pin as the mould is beingopened. This mould half is connected with an operative detaching unitwhich ejects the workpiece from the mould by means of the ejection pins.The movement of the transferjaws 1001 a and 1001 b shown in FIG. 10 ispreferably synchronised with the opening of the mould and the operationof the detaching unit (not shown in the figure), so that, while thedetaching unit is ejecting the ejection pins, the transfer jaws, or atleast the jaw located on the same side of the mould as the detachingunit, pushes the axes over the same distance and in the same direction.In this situation, the movement of the transfer jaws contribute to theremoval of the workpiece from the mould, and no unnecessary mechanicalstains will be exerted on the workpiece in the step where it is removedfrom the mould.

The ejection pins are preferably located in the fastening members of theworkpiece, since they are not intended to remain the final workpiece.FIGS. 11a and 11 b show preferred ways of placing the ejection pins 1101and 1102 in the fastening members. The fastening members may alsocomprise other mechanical designs 1103, 1104 and 1105 which contributeto the alignment of the workpiece in any subsequent process step.

The description above does not take any stand to which way the rawmaterial is introduced in the workpiece. The material to be injectionmoulded flows into the mould from the plastication unit through a givenpouring channel. The positioning of the pouring channel relative to theone or more workpieces can notably influence the quality of the productsprepared in the process. Especially in the production of opticalproducts, such as protective windows for displays, one must payattention to even distribution of the material in the mould, optimallylaminar material flow in the mould, absence of mechanical strains in theworkpiece after injection moulding and to a flawless material surface.

FIG. 12 shows two mutually optional positions of the pouring channel.The top of the figure shows the pouring channel 1201 located between twoadjacent work-pieces, in the centre of the area defined by the chains301 and 302. The material fed from the primary pouring channel firstflows into the flow ducts 1202, relatively large in cross-section, forthe material to fill them up completely before flowing through aplate-like secondary pouring channel 1203 to the actual service member.This arrangement provides a good laminar flow in the service member. Theoutermost end of the flow channel preferably extends beyond thesecondary pouring channel to prevent the material which is coming fromthe very tip of the plastication unit and possibly has been oxygenatedduring the preceding injection-moulding step, or has otherwise alteredproperties, from flowing to the service member. It should also be notedthat the workpieces have lower fastening members 311 at locations as faras possible from the point where the material flows to the servicemember. The lower fastening members 311 act as air pockets, throughwhich the gaseous substances can escape from the mould and make way forthe raw material. The material which has first flowed into the mould,and which may cause surface errors on the mould because it cools whileflowing, also ends up in the lower fastening members 311. Here, at thelower fastening members, these errors will do no harm, because they willnot remain in the final product, i.e. the service member.

The bottom of FIG. 12 shows an optional position 1210 of the pouringchannel The pouring channel is now located in the middle of a group offour workpieces, and then four workpieces can be simultaneously producedin one single injection-moulding step. The material flows into theworkpieces through channels 1211 and 1212. For the pouring channel atthe axis not to impede the forming of the fastening members and thepartial removal of the workpieces from the transport arrangement insubsequent production process steps, it is thus advantageous to use a“hot channel”, and then no material will remain in the workpieces at thepouring channel 1210. The hot channel may be extended all the way to theservice members, and then no material will remain at the channels 1211and 1212 either. The material path disposed as a channel system 1210,1211 and 1212 can also be formed such that the material first flows intoa given flow channel and only from there through a given secondarypouring channel to the service member, so that the flow in the servicemember will be adequately laminar.

The transport arrangement based on axes, which may also use ejectionpins for alignment, is perfectly suitable for multi-step injectionmoulding i.e. production processes in which a given workpiece is formedas a result of two or more separate injection-moulding steps. Theapplication of the invention to an exemplifying two-stepinjection-moulding process is described below, where two-colouredprotective windows for mobile phone displays are produced.

FIG. 13a shows two successive workpieces in a band of successiveworkpieces, where two chains 301 and 302 are used between theworkpieces. The direction of movement of the band in the figure is fromthe top towards the bottom. The upper workpiece has been subjected to afirst injection-moulding step and the lower workpiece has additionallybeen subjected to a second injection-moulding step. In the upperworkpiece, the diagonal lines indicate the material injection-moulded inthe first injection-moulding step, and in the lower workpiece, theinclined lines indicate the material injection-moulded in the secondinjection-moulding step.

The upper workpiece comprises two annular service members 1303 and 1304,into which material has been fed through a pouring channel 1305 locatedin the middle of the area defined by the support wires. The “background”of the mould, i.e. the portion through which no material is fed, alsocomprises recesses, which subsequently form the ejection pins 1308 inthe workpiece. For the sake of simplicity, the figure shows but a smallnumber of ejection pins, however, they may naturally be provided also inother parts of the workpieces.

In the lower workpiece, a continuous central portion 1313 and 1314 hasbeen injection moulded within each annular service member formed in thefirst step. The material has been introduced in the central partsthrough a primary pouring channel 1315 in the middle of an area definedby the support wires, through secondary pouring channels. 1316 and 1317,and also through flow channels 1318 and 1319 located between these. At agiven location of the edge of the annular service members, space hasbeen reserved for the secondary pouring channels in the firstinjection-moulding step. Air pockets have been left at given locationsof the edge of the annular service members also in the firstinjection-moulding step, and in the second injection-moulding step,tongues 1320 will be formed in these air pockets. The aim of using airpockets is to achieve the best optical quality possible in the centralportion. The material typically used in the first injection-mouldingstep is non-transparent, and free space for the secondary pouringchannels 1316 and 1317 and also for the air pockets 1320 will be leftbehind this material so that the material solidified in the secondarypouring channels and in the air pockets in the second injection-mouldingstep will be invisible. FIG. 13b shows a cross-sectional view of theworkpieces in the plane indicated by the dashed line 1321.

Injection moulding is known as a process that allows the production ofhigh-precision pieces. One result of this is that the ejection pins 1308produced in the first injection-moulding step are perfectly suitable foraligning the workpiece exactly at the desired location for anotherinjection-moulding step. On the other hand, the axes and the transferjaws gripping these ensure that the workpieces can be very easilytransferred from one injection-moulding step to another. The embodimentshown in FIG. 13a even allows complex nested moulds, rotation moulds ormoulds reciprocating in linear movement between the process steps to betotally avoided, such moulds having been conventionally required inmulti-step injection moulding. The method may use a mould with twocavities, whose upper cavity has been designed for producing annularservice members in the first injection-moulding step and whose lowercavity has been designed for producing central portions in the secondinjection-moulding step. Of course, it is possible to use two separatemoulds placed in succession in the process. The invention does not byany means restrict the number of successive injection-moulding steps inmulti-step injection moulding, so that moulds with more cavities or agreater number of moulds can be used instead of a mould with twocavities or of two successive moulds.

The process in FIG. 13a can very easily be converted to single-stepinjection moulding by using a mould with two cavities (or two successivemoulds with one single cavity), the cavities being identical and bymoving the band of successive workpieces forwards over the distance oftwo workpieces after each injection-moulding operation. In terms ofproduction techniques, it is very advantageous to be able to use thesame injection-moulding machine for the production of different productsby merely replacing the mould/moulds.

High-precision alignment is useful also in other kinds of productionprocess steps. These steps include the attachment of colour films toworkpieces or processing colour films fixed to bodies. A known methodfor combining a colour film with a product to be injection moulded issuch in which the colour film is placed in the mould before theinjection moulding and the injection-moulded material adheres to thecolour film during solidification. The drawback of this method is that,although the colour film would comprise transparent areas in order toform transparent zones, say, in the protective window of a display, thefriction between the film and the injection-moulded material and theirdifferent thermal expansion characteristics will impair the opticalquality of the transparent area in the final product.

FIG. 14 is a schematic view of a mould 1401, whose size corresponds to amulti-step injection mould with three cavities. For the sake of clarity,the mould is shown only from the rear side, i.e. the side not facing theplastication unit. In the first cavity 1402, such parts of the workpieceare injection moulded on whose surface the colour film 1403 is intendedto remain in the final product. For this purpose, the colour film 1403is run in the mould as a continuous band in a manner known per se. Inthe third cavity 1404, such a part of the workpiece is injection mouldedwhich is intended to be transparent, i.e. whose surface must not becovered, at least not by a colour film part in the finished product.However, the mould does not comprise any second, i.e. central cavity,but instead, in the area 1405, there is a laser cutting head, which bylaser cutting removes the portion of the colour film from thesemi-finished workpiece which would remain at the location of thetransparent zone. Other methods known per se can be used instead oflaser cutting to remove excess parts of the colour film.

FIG. 15 is a schematic view of a different kind of method for makingcolour-film impression on workpieces. The band 1501 of workpiecesattached to the axes moves from the left to the right in the figure. Ata certain point of the production process, a cutting and printing head1502 is provided so that the colour film band 1503 passes between thisand the band of workpieces 1501. When a given workpiece reaches thecutting and printing head 1502, it performs a series of verticalmovements, while the cutting blades 1504 cut a piece with the desiredshape and size from the colour film band 1503 and the printing surfaces1505 press it into contact with the surface of the workpiece. The lowersurface of the colour film is coated with glue, by means of which thedesired colour film pattern adheres into position on the workpiece. Atransport arrangement based on axes ensures that the workpieces areexactly aligned below the cutting and printing head 1502, so that thecolour film adheres with high precision only to the desired areas of theworkpiece.

In the discussion above it has not been considered thatinjection-moulded bodies shrink to some extent while cooling. Since thedistance between the axes is constant in the chain, shrinkage of aworkpiece attached to two successive axes in a direction perpendicularto the axes will generate strain in the workpiece, the axes and thechains. FIGS. 16a, 16 b and 16 c show a number of arrangements thatenable detrimental shrinkage effects to be prevented. In FIG. 16a, thefastening member in the workpiece has been formed with a curve 1601 orany other mechanical design with such strength properties that itstretches when the workpiece shrinks. In this way, the effect ofshrinkage is confined under control to a given point of the workpiece.FIG. 16b shows a bushing located at the end of the axis 305 for theattachment of the axis to the chain; integrated in the bushing is asleeve 1602 made of an elastic material, which yields as the workpieceshrinks. FIG. 16a shows a fastening member in the chain having anelliptic hole 1603 in which the axis 305 is allowed to move freely overa given distance in the longitudinal direction of the chain.

Only such embodiments have been described above which comprise twochains and a continuous axis between these. An embodiment of theinvention is conceivable which comprises one single chain, provided thatthe axes can be attached to this with adequate firmness. In addition,embodiments of the invention are conceivable, which comprise three ormore chains in parallel. Depending on the moulds used, identical ordifferent products can be injection moulded between the differentchains.

FIG. 17 is a schematic view of a solution in which the axes between twochains is discontinuous, consisting of two axis ends 1701 and 1702. Inboth these ends, the extremity facing the workpiece comprises afastening design, in which a specific insert 1703 made of e.g. metal orhard plastic is placed before the injection moulding. When the workpiece1704 is injection moulded, the material adheres to the insert 1703during solidification so that the cent between the workpiece and theaxis is provided at least partly by means of the insert after theinjection-moulding operation.

The embodiments of the invention described above are given by way ofexample, and they have no limiting effect on the invention. Variousadditional features of the invention have been described in variousconjunctions; these additional features can be freely combined to formvarious combinations.

What is claimed is:
 1. A method for treating workpieces to be injection moulded in a production process, comprising steps for a) forming a workpiece by injection moulding so that during the injection moulding, the workpiece is attached to a given elongated transport arrangement by a first fastening member and a second fastening member, b) moving the workpiece forward in the production process by means of the elongated transport arrangement, c) detaching the first fastening member of the workpiece from the elongated transport arrangement, and d) shifting the workpiece supported by the second fastening member remaining between this and the transport arrangement into position where the workpiece is substantially outside a plane defined by the transport arrangement to which the workpiece is fastened.
 2. A method as defined in claim 1, wherein in step a), the fastening members are formed in the workpiece, at least part of the fastening members enclosing at least partly a given axis included in the transport arrangement.
 3. A method as defined in claim 2, wherein in step c), the first fastening member is detached, which partly enclosed a given axis in the transport arrangement, by detaching the enclosing portion from the axis by pressing.
 4. A method as defined in claim 1, wherein in step a), the fastening members are formed in the workpiece, at least part of which lie on a given axis in the transport arrangement by force of gravity.
 5. A method as defined in claim 4, wherein in step c), the transport arrangement is shifted into a position where the first fastening member having lain on the axis is drawn by force of gravity into a different direction than towards the axis.
 6. A method as defined in claim 1, wherein after step d), the workpiece attached to the transport arrangement by the second fastening member is subjected to surface treatment by immersion into a surface-treatment agent without the transport arrangement getting into contact with the surface-treatment agent.
 7. A method as defined in claim 1, wherein in step a), the workpiece is formed by multi-step injection moulding so that in the first injection-moulding step, the workpiece is attached to a given elongated transport arrangement, by means of which it is transferred to the following injection-moulding step.
 8. A method as defined in claim 1, wherein between steps a) and b), it comprises a step for detaching the injection-moulded workpiece from the injection mould by pressing, simultaneously and into the same direction, given ejection pins in the workpiece and those parts of the transport arrangement to which the workpiece is attached.
 9. A method as defined in claim 1, wherein it comprises, after step b), a step for exact positioning for aligning the workpiece accurately with the parts of the transport arrangement to which the workpiece is attached.
 10. A method as defined in claim 9, wherein the step for exact positioning of the workpiece comprises a step for removing film-like material from the workpiece by cutting.
 11. A method as defined in claim 9, wherein the step for exact positioning of the workpiece comprises a step for fixing at least one pattern of film-like material to the workpiece.
 12. A method as defined in claim 1, further comprising before step a) a step for placing an insert in the injection mould, the insert having been adapted to be fastened to the transport arrangement, and the workpiece being formed in step a) so as to be fastened to the insert.
 13. An apparatus for treating workpieces to be injection moulded in a production process, the apparatus comprising a mould for producing workpieces by injection moulding an elongated transport arrangement for moving the injection-moulded workpieces forwards in the production process; the mould having been disposed in the apparatus to form first and second fastening members in the workpieces for attachment of the workpieces to the transport arrangement, means for detaching the first fastening member of the workpieces from the transport arrangement while the second fastening member remains attached, means for shifting such a workpiece, whose first fastening member fastened to the transport arrangement has been detached, into a position relative to the transport arrangement to which the workpiece is fastened, where it is substantially outside a plane defined by the transport arrangement.
 14. An apparatus as defined in claim 13, wherein the transport arrangement comprises at least one elongated band or chains and a plurality of axes transversely attached to this the mould has been disposed to form fastening members in the work-pieces for fastening each workpiece to two successive axes the means for detaching the first fastening member of the workpiece from the transport arrangement have been disposed to detach the first fastening member of the workpiece from one of the two axes to which the workpiece is fastened.
 15. An apparatus as defined in claim 14, wherein the means for shifting a workpiece whose first fastening member fastened to the transport arrangement has been detached into a position relative to the transport arrangement where it is substantially outside a plane defined by the transport arrangement comprise means for shifting the transport arrangement in a position where each workpiece is suspended by one axis in a direction substantially perpendicular to the transport arrangement.
 16. An apparatus as defined in claim 15, wherein it comprises a surface-treatment vessel for wetting the workpiece suspended substantially perpendicularly to the transport arrangement with the surface-treatment agent provided in the surface-treatment vessel.
 17. An apparatus as defined in claim 14, wherein the axes comprise fastening designs for fastening the axes to the elongated band or chain and/or for fastening the workpieces to the axes.
 18. An apparatus as defined in claim 14, further comprising means for ensuring a play for the axes in the longitudinal direction of the band or the chain as they are fastened to the elongated band or chain.
 19. An apparatus as defined in claim 13, further comprising, connected with the mould, transfer jaws disposed to transfer the transport arrangement when the mould is open, and to release their grip of the transport arrangement and to move in a direction opposite to the direction of movement of the transport arrangement when the mould is closed.
 20. An apparatus as defined in claim 19, further comprising means in the mould for forming ejection pins in the workpiece and a detaching unit in connection with the mould for removing the workpiece from the mould by pressure of the ejection pins, the detaching unit and at least one of the transfer jaws having been disposed to operate in synchronisation so that, as the detaching unit ejects the ejection pins in a given direction, said transfer jaw presses the transport arrangement in the same direction.
 21. An apparatus as defined in claim 13, further comprising a pouring channel in connection with the mould for feeding material into the mould, with the spine formed at the pouring channel being one of the means for fastening the workpiece to the transport arrangement.
 22. An apparatus as defined in claim 13, further comprising, in connection with the mould, a hot pouring channel for feeding material into the mould so that no sprue is formed at the pouring channel.
 23. An apparatus as defined in claim 13, wherein the mould comprises at least two mould cavities in succession in the direction of movement of the transport arrangement to carry out multi-step injection moulding, the apparatus comprising means for fitting a semi-finished workpiece formed in the first mould cavity into position in the second mould cavity in alignment with the transport arrangement.
 24. An apparatus as defined in claim 13, further comprising means for adding a film-like material on the surface of the workpiece, and means for fitting the workpiece, in alignment with the transport arrangement, into position in the process step where film-like material is applied to or removed from the surface of the workpiece. 